The present invention relates to a thermal insulator cabinet applicable for refrigerators, freezers, insulating containers, and storage containers as well as to a method of manufacturing the same.
Development of high-performance apparatus and equipment has been required for the energy-saving purpose. Improvement in performance of thermal insulators by the vacuum insulating technique is essential to improve the performance of thermal insulator cabinets.
Vacuum insulating panels are a typical example of vacuum insulators used for refrigerators. The vacuum insulating panel is manufactured by covering a continuous-spacing core member, such as open-cell hard urethane foam, with a gas-barrier metal-plastic laminate film and evacuating and packing the covered core (for example, Japanese Laid-Open Patent Publication Hei 7-293785). The vacuum insulating panel is further processed to have a double structure when being applied to the thermal insulator cabinet of, for example, refrigerators. The process sticks the vacuum insulating panels to a container of the cabinet and injects an expandable urethane resin for foam molding.
Another technique applied to manufacture the vacuum insulator cabinets is evacuation (for example, Japanese Laid-Open Patent Publication Hei 6-174186 and 7-148752). The thermal insulator cabinet is filled with the material having a closed-cell structure or a continuous-spacing structure and evacuated with a vacuum pump. In another example, a vacuum indicator is used to monitor a variation in thermal insulating performance with time and carry out evacuation according to the requirements (Japanese Laid-Open Patent Publication Hei 7-148752).
The foam molding process may be applied to control the gas constituents in the cells, which affect the thermal insulating ability of expanded insulators, and manufacture the vacuum insulators (for example, Japanese Laid-Open Patent Publication Hei 7-53757 and 7-53769). In these proposed methods, a carbon dioxide-fixing agent is added to the resin material. The carbon dioxide-fixing agent fixes carbon dioxide existing in the cells in the carbon dioxide-blown resin insulators, so as to reduce the pressure in the cells or evacuate the cells and improve the thermal insulating ability.
A typical procedure of manufacturing the vacuum insulating panel discussed above prepares a block of open-cell hard urethane foam, cuts the block into a core of an arbitrary size, and packs the core in vacuo. The vacuum insulating panels should be manufactured separately before being combined with standard expanded insulators. This also requires the process of sticking the vacuum insulating panels to the container of the thermal insulator cabinet. It is accordingly not preferable from the viewpoints of productivity, workability, and cost. Since the vacuum insulating panels are combined with expanded insulators, there is inevitably a part of the surface of the thermal insulator cabinet not covered with the vacuum insulating panel. This causes deterioration of the vacuum insulating ability. The vacuum insulating panels do not have any means for recovering the worsened degree of vacuum of the vacuum insulating panels with time. This lowers the thermal insulating ability and causes the poor long-term reliability.
Unlike the manufacturing method with the vacuum insulator panels, the method of manufacturing a thermal insulator cabinet by the evacuation technique does not require the separate manufacturing process or the sticking process, but enables the whole cabinet to be set in the vacuum insulating state. This method, however, requires a vacuum pump for evacuation and a long-time evacuation is essential for the sufficient degree of vacuum. This results in the poor productivity. In order to maintain the thermal insulating ability over time, the evacuation with a vacuum pump should be continued or otherwise carried out repeatedly based on the monitored degree of vacuum. This causes the poor workability and the poor long-term reliability.
The method of foam molding the vacuum insulators has excellent productivity and ensures the long-term reliability by fixation of carbon dioxide. Addition of the carbon dioxide-fixing agent to the resin material may cause fixation of carbon dioxide to start before the resin is completely blown with carbon dioxide. This may result in contraction of the foamed resin that has not yet been completely cured. An increase in amount of carbon dioxide to prevent this problem increases the required amount of the carbon dioxide-fixing agent and lowers the productivity.